This invention relates to a liquid-immersed disc brake, primarily for a vehicle, and of the general kind which comprises a housing containing at least one friction element rotatable with a member to be braked and providing a first braking surface, a torque resisting member providing a second braking surface adjacent said first surface and which is relatively stationary during braking, actuator means operable to bring the first and second surfaces into braking engagement, and means for supplying cooling liquid to the housing in cooling relationship with said surfaces.
Brakes of the aforesaid general kind are primarily used in tractors and other off-highway vehicles and the vehicle gearbox oil is then conveniently used as the cooling liquid. Although a relatively large quantity of oil is required for cooling the brake during prolonged and/or heavy periods of braking, it is desirable to reduce the amount of oil present in the housing at other times in order to minimise the well-known parasitic oil drag effects and thus avoid excessive brake running clearances and the consequent long brake pedal travel and/or high actuation input forces. In order to reconcile these conflicting liquid requirements, various proposals have already been made for ensuring that the supply of cooling liquid to the braking surfaces is substantially greater during braking than in the non-applied condition of the brake.
Examples of such proposals are to be found in our earlier European specifications Nos. 0315443 and 0315444 and rely upon braking torque to actuate a valve incorporated in a lug provided on a pressure plate of the brake to control the flow of cooling liquid. This arrangement is generally satisfactory in operation but involves the use of a non-standard pressure plate to house the valve, which itself needs to be robust to withstand the continual impacts with the torque-taking abutment. This arrangement is therefore somewhat expensive to produce.